Editing Hippocampus (section)

=== Role in spatial memory and navigation ===
{{Main|Place cell}}
[[File:Place Cell Spiking Activity Example.png|thumb|300px|right| Spatial [[firing pattern]]s of eight [[place cell]]s recorded from the [[#Structure|CA1]] layer of a rat. The rat ran back and forth along an elevated track, stopping at each end to eat a small food reward. Dots indicate positions where [[action potential]]s were recorded, with color indicating which neuron emitted that action potential.]]
[[File:HIPO-33-533-g013.jpg|thumb|300px|Hippocampal connections in spatial cognition]]
There are several types of [[Navigation#Navigation in spatial cognition|navigational]] cells in the brain that are either in the hippocampus itself or are strongly connected to it. They include the [[place cell]]s, [[speed cells]] present in the [[entorhinal cortex|medial entorhinal cortex]], [[head direction cell]]s, [[grid cell]]s, and [[boundary cell]]s.<ref name=Moser2008 /><ref>{{cite journal | vauthors = Solstad T, Boccara CN, Kropff E, Moser MB, Moser EI | title = Representation of geometric borders in the entorhinal cortex | journal = Science | volume = 322 | issue = 5909 | pages = 1865–1868 | date = December 2008 | pmid = 19095945 | doi = 10.1126/science.1166466 | ref = refSolstad2008 | s2cid = 260976755 | doi-access =  | bibcode = 2008Sci...322.1865S }}</ref> Together these cells form a network that serves as [[spatial memory]].

The first of these types of cell discovered in the 1970s were the place cells, which led to the idea of the hippocampus acting to give a neural representation of the environment in a [[cognitive map]].<ref name="O'Keefe" /> When the hippocampus is dysfunctional, orientation is affected; people may have difficulty in remembering how they arrived at a location and how to proceed further. Getting lost is a common symptom of amnesia.<ref>{{cite journal | vauthors = Chiu YC, Algase D, Whall A, Liang J, Liu HC, Lin KN, Wang PN | title = Getting lost: directed attention and executive functions in early Alzheimer's disease patients | journal = Dementia and Geriatric Cognitive Disorders | volume = 17 | issue = 3 | pages = 174–180 | year = 2004 | pmid = 14739541 | doi = 10.1159/000076353 | ref = refChiu2004 | s2cid = 20454273 }}</ref> Studies with animals have shown that an intact hippocampus is required for initial learning and long-term retention of some spatial memory tasks, in particular ones that require finding the way to a hidden goal.<ref>{{cite journal | vauthors = Morris RG, Garrud P, Rawlins JN, O'Keefe J | title = Place navigation impaired in rats with hippocampal lesions | journal = Nature | volume = 297 | issue = 5868 | pages = 681–683 | date = June 1982 | pmid = 7088155 | doi = 10.1038/297681a0 | ref = refMorris1982 | s2cid = 4242147 | bibcode = 1982Natur.297..681M }}</ref><ref>{{cite journal | vauthors = Sutherland RJ, Kolb B, Whishaw IQ | title = Spatial mapping: definitive disruption by hippocampal or medial frontal cortical damage in the rat | journal = Neuroscience Letters | volume = 31 | issue = 3 | pages = 271–276 | date = August 1982 | pmid = 7133562 | doi = 10.1016/0304-3940(82)90032-5 | ref = refSutherland1982 | s2cid = 20203374 }}</ref><ref>{{cite journal | vauthors = Sutherland RJ, Weisend MP, Mumby D, Astur RS, Hanlon FM, Koerner A, Thomas MJ, Wu Y, Moses SN, Cole C, Hamilton DA, Hoesing JM | title = Retrograde amnesia after hippocampal damage: recent vs. remote memories in two tasks | journal = Hippocampus | volume = 11 | issue = 1 | pages = 27–42 | year = 2001 | pmid = 11261770 | doi = 10.1002/1098-1063(2001)11:1<27::AID-HIPO1017>3.0.CO;2-4 | ref = refSutherland2001 | s2cid = 142515 }}</ref><ref>{{cite journal | vauthors = Clark RE, Broadbent NJ, Squire LR | title = Hippocampus and remote spatial memory in rats | journal = Hippocampus | volume = 15 | issue = 2 | pages = 260–272 | year = 2005 | pmid = 15523608 | pmc = 2754168 | doi = 10.1002/hipo.20056 | ref = refClark2005 }}</ref>

Studies on freely moving rats and mice have shown many hippocampal [[neuron]]s to act as [[place cell]]s that cluster in [[Place cell#Place fields|place fields]], and these fire bursts of [[action potential]]s when the animal passes through a particular location.<ref name="Eichenbaum_2017">{{cite journal | vauthors = Eichenbaum H | title = The role of the hippocampus in navigation is memory | journal = Journal of Neurophysiology | volume = 117 | issue = 4 | pages = 1785–1796 | date = April 2017 | pmid = 28148640 | pmc = 5384971 | doi = 10.1152/jn.00005.2017 }}</ref>
Hippocampal place cells interact extensively with head direction cells, whose activity acts as an inertial compass, and conjecturally with grid cells in the neighboring entorhinal cortex.<ref>{{cite book | vauthors = Taube JS, Yoder RM | chapter = The impact of vestibular signals on cells responsible for orientation and navigation. | doi = 10.1016/B978-0-12-809324-5.23894-7 | veditors = Fritzsch B |title=The Senses; Volume 6: Vestibular System and Balance |date=2020 | pages = 496–511 |publisher=Elsevier Science & Technology |location=San Diego |isbn=978-0-12-805409-3 |edition=2nd }}</ref> Speed cells are thought to provide input to the hippocampal grid cells.<ref>{{cite web | vauthors = Moser MB | author-link = May-Britt Moser | title = Grid cells, place cells and memory. | work = Nobel Lecture | date = 7 December 2014 | url = https://www.nobelprize.org/uploads/2018/06/may-britt-moser-lecture-slides.pdf | publisher = The Nobel Foundation | location = Stockholm, Sweden }}</ref> This place-related neural activity in the hippocampus has also been reported in monkeys that were moved around a room whilst in a restraint chair.<ref>{{cite journal | vauthors = Matsumura N, Nishijo H, Tamura R, Eifuku S, Endo S, Ono T | title = Spatial- and task-dependent neuronal responses during real and virtual translocation in the monkey hippocampal formation | journal = The Journal of Neuroscience | volume = 19 | issue = 6 | pages = 2381–2393 | date = March 1999 | pmid = 10066288 | pmc = 6782547 | doi = 10.1523/JNEUROSCI.19-06-02381.1999 | ref = refMatsumura1999 }}</ref> However, the place cells may have fired in relation to where the monkey was looking rather than to its actual location in the room.<ref>{{cite journal | vauthors = Rolls ET, Xiang JZ | title = Spatial view cells in the primate hippocampus and memory recall | journal = Reviews in the Neurosciences | volume = 17 | issue = 1–2 | pages = 175–200 | year = 2006 | pmid = 16703951 | doi = 10.1515/REVNEURO.2006.17.1-2.175 | ref = refRolls2006 | s2cid = 147636287 }}</ref> Over many years, many studies have been carried out on place-responses in rodents, which have given a large amount of information.<ref name=Moser2008 /> Place cell responses are shown by [[pyramidal cell]]s in the hippocampus and by [[granule cell]]s in the [[dentate gyrus]]. Other cells in smaller proportion are inhibitory [[interneuron]]s, and these often show place-related variations in their firing rate that are much weaker. There is little, if any, spatial topography in the representation; in general, cells lying next to each other in the hippocampus have uncorrelated spatial [[firing pattern]]s. Place cells are typically almost silent when a rat is moving around outside the place field but reach sustained rates as high as 40 [[hertz|Hz]] when the rat is near the center. Neural activity sampled from 30 to 40 randomly chosen place cells carries enough information to allow a rat's location to be reconstructed with high confidence. The size of place fields varies in a gradient along the length of the hippocampus, with cells at the dorsal end showing the smallest fields, cells near the center showing larger fields, and cells at the ventral tip showing fields that cover the entire environment.<ref name=Moser2008 /> In some cases, the firing rate of hippocampal cells depends not only on place but also the direction a rat is moving, the destination toward which it is traveling, or other task-related variables.<ref>{{cite journal | vauthors = Smith DM, Mizumori SJ | title = Hippocampal place cells, context, and episodic memory | journal = Hippocampus | volume = 16 | issue = 9 | pages = 716–729 | year = 2006 | pmid = 16897724 | doi = 10.1002/hipo.20208 | ref = refSmith2006 | s2cid = 720574 | citeseerx = 10.1.1.141.1450 }}</ref> The firing of place cells is timed in relation to local [[#Theta rhythm|theta waves]], a [[spatiotemporal]]  process termed [[phase precession]].<ref name="Lian2022">{{cite journal |vauthors=Lian Y, Burkitt AN |title=Learning Spatiotemporal Properties of Hippocampal Place Cells |journal=eNeuro |volume=9 |issue=4 |pages= |date=2022 |pmid=35760526 |pmc=9282168 |doi=10.1523/ENEURO.0519-21.2022 |url=}}</ref><ref name="OKeefe1993">{{cite journal | vauthors = O'Keefe J, Recce ML | title = Phase relationship between hippocampal place units and the EEG theta rhythm | journal = Hippocampus | volume = 3 | issue = 3 | pages = 317–330 | date = July 1993 | pmid = 8353611 | doi = 10.1002/hipo.450030307 | s2cid = 6539236 }}</ref>

Cells with location-specific firing patterns have been reported during a study of people with [[drug-resistant epilepsy]]. They were undergoing an invasive procedure to localize the source of their [[seizure]]s, with a view to surgical resection. They had diagnostic electrodes implanted in their hippocampi and then used a computer to move around in a [[virtual reality]] town.<ref name="Ekstrom">{{cite journal | vauthors = Ekstrom AD, Kahana MJ, Caplan JB, Fields TA, Isham EA, Newman EL, Fried I | title = Cellular networks underlying human spatial navigation | journal = Nature | volume = 425 | issue = 6954 | pages = 184–188 | date = September 2003 | pmid = 12968182 | doi = 10.1038/nature01964 | url = http://memory.psych.upenn.edu/Publications#EkstEtal03 | ref = refEkstrom2003 | access-date = 2013-01-24 | url-status = live | format = PDF | s2cid = 1673654 | citeseerx = 10.1.1.408.4443 | bibcode = 2003Natur.425..184E | archive-url = https://web.archive.org/web/20211020000026/http://memory.psych.upenn.edu/Publications#EkstEtal03 | archive-date = 2021-10-20 }}</ref> Similar [[neuroimaging|brain imaging]] studies in [[Navigation#Navigation in spatial cognition|navigation]] have shown the hippocampus to be active.<ref>{{cite journal | vauthors = Duarte IC, Ferreira C, Marques J, Castelo-Branco M | title = Anterior/posterior competitive deactivation/activation dichotomy in the human hippocampus as revealed by a 3D navigation task | journal = PLOS ONE | volume = 9 | issue = 1 | pages = e86213 | date = 2014-01-27 | pmid = 24475088 | pmc = 3903506 | doi = 10.1371/journal.pone.0086213 | doi-access = free | bibcode = 2014PLoSO...986213D }}</ref> A study was carried out on taxi drivers. London's [[Hackney carriage|black cab]] drivers need to learn the locations of a large number of places and the fastest routes between them in order to pass a strict test known as [[Taxicabs of the United Kingdom#The Knowledge|The Knowledge]] in order to gain a license to operate. A study showed that the posterior part of the hippocampus is larger in these drivers than in the general public, and that a positive correlation exists between the length of time served as a driver and the increase in the volume of this part. It was also found the total volume of the hippocampus was unchanged, as the increase seen in the posterior part was made at the expense of the anterior part, which showed a relative decrease in size. There have been no reported adverse effects from this disparity in hippocampal proportions.<ref name="Maguire">{{cite journal | vauthors = Maguire EA, Gadian DG, Johnsrude IS, Good CD, Ashburner J, Frackowiak RS, Frith CD | title = Navigation-related structural change in the hippocampi of taxi drivers | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | issue = 8 | pages = 4398–4403 | date = April 2000 | pmid = 10716738 | pmc = 18253 | doi = 10.1073/pnas.070039597 | ref = refMaguireFrith2000 | doi-access = free | bibcode = 2000PNAS...97.4398M }}</ref> Another study showed opposite findings in blind individuals. The anterior part of the right hippocampus was larger and the posterior part was smaller, compared with sighted individuals.<ref>{{cite journal | vauthors = Leporé N, Shi Y, Lepore F, Fortin M, Voss P, Chou YY, Lord C, Lassonde M, Dinov ID, Toga AW, Thompson PM | title = Pattern of hippocampal shape and volume differences in blind subjects | journal = NeuroImage | volume = 46 | issue = 4 | pages = 949–957 | date = July 2009 | pmid = 19285559 | pmc = 2736880 | doi = 10.1016/j.neuroimage.2009.01.071 }}</ref>